This application responds to Notice Number (NOT-OD-09-058) entitled: NIH Announces the Availability of Recovery Act Funds for Competitive Revision Applications. The long term goal of this study is to develop improved cancer treatments through modulation of topoisomerase I (topo I), an important target for camptothecin-like chemotherapeutic drugs, and to further elucidate how the p14ARF/topo I complex contributes to the mechanism of cancer and to the therapy response. p14ARF plays a well-established role in the p53 pathway, and also engages in a novel p53-independent interaction with topo I. The interaction requires topo I serine phosphorylation, activates topo I, and enhances cellular sensitivity to camptothecin and related topo I-targeted chemotherapeutic drugs. Cancer cells with reduced topo I phosphorylation lack p14ARF/topo I complexes and are resistant to camptothecin. A better understanding of the regulation of this complex would therefore elucidate the roles of both proteins in cancer, and could lead to improved diagnostic and therapeutic strategies for cancer. The Specific Aims of the parent grant are to (1) Determine the molecular features of the p14ARF/topo I interaction, (2) Define the molecular mechanism of p14ARF-mediated activation of topo I, (3) Determine how frequently abnormalities in p14ARF/topo I complex formation occur in cancer and whether they correlate statistically with clinic attributes of tumors, and (4) Determine the therapeutic potential of p14ARF-mediated therapy sensitization. The revised grant introduces an additional Aim (5) that studies the effects of Spermidine-CoA-based inhibitors of histone acetylation, a class of cancer cell-targeted compounds that inhibit double strand break repair and sensitize cells to camptothecin. The Aim examines how these inhibitors affect topo I alone and in combination with p14ARF and provides a preclinical evaluation of their efficacy as therapy sensitizers in the presence and absence of ARF. The study will employs molecular biology techniques (Aim I), biochemical assays (Aims II and V), immunoprecipitation/western analysis and immunofluorescence (Aim III), and cell culture-based viability assays and human tumor xenograph models in nude mice (Aims IV and V). PUBLIC HEALTH RELEVANCE: This study develops novel approaches based on the p14ARF tumor suppressor and Spermidine-CoA-based inhibitors of histone acetylation to improve cellular responses to topoisomerase I-targeted chemotherapies and reverse therapy resistance, a major obstacle to successful cancer treatment. The study also develops diagnostic tools for identifying therapy responsive tumors and optimizing therapeutic regimens. .